1. Field of the Invention
The present invention relates to an image forming apparatus for reducing a fluctuation of toner density in a developing unit.
2. Description of the Related Art
A two-component developer is a developer including a toner and a carrier. An image forming apparatus develops an electrostatic latent image by causing a frictional electrification by mixing the toner and the carrier, and causing the toner to fly towards a photosensitive member. It is necessary for the toner to be replenished because it is consumed by developing. Also, in order to keep the density of the toner image at a desired density, it is necessary that a proportion between the toner and the carrier (a T/D ratio) to be maintained fixedly. The T/D ratio is an indicator of a toner density in the developing unit.
In accordance with Japanese Patent Laid-Open No. H09-127780, it is proposed that replenishment control in accordance with two-component developer toner density (feedback control), and replenishment control in accordance with a toner consumption amount estimated from an image signal (feedforward control) be switched.
In Japanese Patent Laid-Open No. H09-127780, because toner is replenished in parallel to image formation, when the T/D ratio changes greatly due to toner replenishment during image formation, an unevenness in the density of an image formed on a recording medium may occur. Accordingly, a configuration for replenishing a toner after having first stopped image formation when the toner is significantly insufficient is investigated.